The air many of us breathe poses serious health risks, the World Health Organization says. On Thursday, it added cancer to the list.

Air pollution is a now officially a carcinogen, and there are no caveats about the new classification.

"We know that it is causing cancer in humans," said spokesman Kurt Straif.

In 2010, lung cancer resulting from air pollution took the lives of 223,000 people worldwide. As pollution levels climb, so will the rate of cancer, the WHO said.

And there is only one way to stop it: Clean up the air.

"We can't treat ourselves out of this cancer problem," said Chris Wild, who heads the WHO's cancer research wing, the International Agency for Research on Cancer.

Cleaner air would also have other health benefits. Air pollution increases the risk of bladder cancer, the IARC said. It has been known for a while that it contributes to heart disease and respiratory ailments.

The problem is global, but people in developing countries with large populations and booming manufacturing sectors with few pollution controls are said to be particularly at risk.

The agency decided upon the official classification of outdoor air pollution as carcinogenic after reviewing the latest scientific writings and coming to the conclusion that the evidence was ample.

The classification is an important step, said Dr. Christopher Wild, director of the IARC.

"There are effective ways to reduce air pollution and, given the scale of the exposure affecting people worldwide, this report should send a strong signal to the international community to take action without further delay."

The IARC called air pollution the most widespread environmental carcinogen and the worst.